I can live with the clunky UI, but not with data loss. After a short time it began to pop up nonsensical error messages ("Not one tab was not synchronized" or something). At some point it never finished loading, and all my saved tabs were lost. Avoid.
Please, update Firefox to latest version v61 and after that update addon to STG v3.0 (not experimental). In this version I implement hide tabs api, switch between groups and not close tabs
